The woman's two ovaries of the egg maturation takes place. The woman is born with the precursors of all the eggs she produces in her lifetime, in contrast to the man who continually produce sperm in her fertile age. When asophisticated interaction of hormones (see Menstruation and klimakterium) mature egg cells that turn into the mature eggs. Each 28 days (on average) released an egg from one of the two ovaries from mature folikel. The rule is released only one egg, and is usually alternating the two ovaries to produce eggs. If released more than an egg, it can lead to multiple pregnancy (twins).

When foliklen burst, the egg is released to the abdominal cavity, where it picked up by Cilium on eggshells leaders. From there it from the uterus. Fertilization is usually in the thickest part of the egg-head (ampulla). Already here begins cell division. When the cluster of cells whenuterus, which is usually around 16 cells. This is called morulastadiet (morula: Latin for mulberry, which is similar to the cells). Then happens reproduction (nidationen), where the cluster of cells is growing fast in livmoderslimhinden and form an embryo.

Sædcellerne formed in sædkanalerne in testis, where they headed to sædblæren, which sits blærehalskirtlen.

There must be only a single sperm to fertilize an egg, but it is a relatively small portion sperm, they still reach the egg. Therefore, we speak of reduced sperm quality, if there are fewer than 10 million sperm per. ml. semen.